The man Russian police believe was the suicide bomber who killed 14 people in a blast on the St Petersburg metro this week developed an interest in Islam and soon after traveled to Turkey, two people who know him told Reuters.

The two people said they did not know for sure if the man, Akbarzhon Jalilov, went on from Turkey to neighboring Syria. Turkey has been routinely used by radical Islamists as a route into areas of Syria controlled by the Islamic State group.

If Jalilov had been in Syria, that would expose a major gap in Russia's counter-terrorism procedures, which rely heavily on identifying anyone who has been with militants in Syria and stopping them from returning to Russia, or arresting them.

RUSSIAN security forces have killed two armed militants who had been trained by Islamic State and were planning a series of “terrorist crimes”, Russian news agencies report.

The National Anti-Terror Committee said on Saturday the two men had been killed in the Stavropol region of southern Russia after a shootout with security forces who had tried to stop their car.

“The bandits have been preliminarily identified: one was the leader of a cell, trained in Islamic State camps and returned to Russia to carry out terrorist acts. The other was an active cell member,” Interfax news agency quoted the committee as saying.

Russia has been on heightened alert after a suicide bomber killed 16 people in an attack on the St Petersburg metro earlier this month.

Russia’s Federal Security Service said on Friday a gunman had burst into one of its regional offices in the far east of the country and opened fire, killing one of its employees and a visitor.